Forming subterranean cavities by solution mining



March 28, 1961 R. c. ALLRED ET AL 2,976,690

FORMING SUBTERRANEAN CAVITIES BY SOLUTION MINING FiledvMa RM? OOLR THLU Y WSAM M Twww ciad/U .HON A ,mmH mw Y B FORMING SUBTERRANEAN CAVITIES BY SOLUTIGN MINING Raymond C. Allred, DArcy A. Shock, and John D. Sudbury, Ponca City, Okla., assignors to Continental Oil Company, Ponca City, Okla., a corporation of Delaware Filed May 7, 1959, Ser. No. 811,634

Claims. (Cl. 61-.5)

This invention relates to methods of forming subterranean cavities in salt beds and particularly concerns techniques of solution mining for achieving such purposes.

Solution mining techniques have heretofore been used to form a cavity in underground salt beds, but generally the cavity which is formed is quite large and of uncontrolled proportions. The diameter of the cavity is much larger than the height of the cavity. Such cavity cannot be used as a place for the disposal of radioactive Waste from reactor operations because these Wastes evolve heat when stored in large diameter quantities. A preferred cavity would be one which was of limited diameter and of relatively unlimited length. For example, a cavity of 10 feet in diameter and 100 feet or more in length would be suitable for the disposal of radioactive waste. However, the ordinary solution mining of underground salt beds does not produce such a cavity.

An object of this invention is to provide a method for forming cavities of controlled proportions in underground salt beds. Another object is to provide methods for the underground solution mining of salt beds whereby cavities of controlled diameter and height are produced. A further object is to provide methods for forming connected superposed cavities of controlled proportions in underground salt beds. These and other objects will be more apparent from the detailed description of the invention.

'Ihe method of this invention may be practiced by providing inlet and outlet conduits to the underground salt bed and then carrying out the particular techniques by which the controlled proportion cavity or cavities are formed. This is done by introducing water into the salt bed via the inlet conduit. The Water dissolves salt and a brine is formed. The brine is removed from the forming cavity via the outlet conduit. This brine is then repeatedly recirculated via the inlet conduit into the cavity which is being formed. The total amount of water which is introduced for the purpose of forming the cavity is an amount sutiicient to form a cavity of predetermined or desired diameter. After the total amount of water has been introduced and the brine has been recirculated (Water and brine usually being introduced together into the bed for convenience), until it has become saturated with salt, the recirculation is discontinued. The saturated brine is then permitted to remain in the cavity. The inlet and outlet conduits are elevated to points above the level of the saturated brine and the process steps related heretofore are repeated. A plurality of connected and superposed cavities lled with saturated brine are thus formed in the salt bed. The saturated brine is then removed and the cavities then used for storage purposes.

Figure l illustrates in schematic form how the method of this invention may be carried out in forming a series of connected superposed cavities within an underground salt formation.

Referring to Figure 1, cavities 1 and 2 have been Patented Mar. 28, '1961 formed in the salt formation. Cavity 3 illustrates how the individual cavity (such as cavitiesl and 2) of the series are formed, and numeral 4 indicates Where cavity 4 in the series will be formed as the next step. A saturated brine solution is present in connected cavities 1 and 2. In forming cavity 3, the inlet and outlet conduits (whose terminal underground ends were originally located in lower positions in forming cavities 1 and 2), are located as shown in Figure l. Fresh water is introduced down valved inlet conduit 11 through outlet or nozzle ports 12 located at the bottom of the inlet conduit. A plurality of outlet ports 12 are located around the circumference of the tubular inlet conduit 11 near the bottom thereof. The bottom of tubular inlet conduit 11 is sealed except for outlet ports 12. As the fresh water contacts the salt formation it dissolves the salt. The continuing ow of water down the inlet conduit enlarges the cavity being formed about the outlet ports. Brine which is formed is pumped, by means not shown herein, up outlet conduit 12. This brine, Which is ordin-arily unsaturated with respect to salt, is pumped through recycled line 13 into inlet conduit 11 by which it is returned to the forming cavity. Usually, the recirculating brine joins fresh water and the two are passed together down inlet conduit 11. The fresh water is continuously introduced down the inlet conduit until the total amount has been added. In this embodiment a total of 36,300 gallons are employed, this amount being sufficient to form a cylindrical cavity approximately l0 feet in diameter and l0 feet in height. (Cavities of other proportions may, of course, be formed with the departing from the claimed method of this invention.)

After all of the fresh water has been introduced the brine continues to be recirculated until it has become saturated with respect to salt. At the usual operating water temperature water will dissolve approximately 35 pounds per pound of water. After the brine has become saturated with salt it is no longer recirculated and is permitted to remain in the cavity which has been formed. The inlet and outlet conduits are then raised above the level of the saturated brine in the cavity and the process steps involved informing another cavity above cavity 3 are repeated. The distance by which the inlet and outlet cavities are raised may be from one-half to one cavity diameter. The channel(s) which is formed in the salt bed when the inlet and outlet conduits are raised (for the purpose of forming the next higher cavity), forms a connecting passageway between the individual superposed cavities. By repeating the cavity forming steps, raising the conduits, and then repeating again the cavity forming steps, et seq., a plurality of superposed and connected cavities may be formed to the desired height. Proper selection of the amount of water used in forming the individual cavity Will goven the diameter thereof. It is thus apparent that a cavity, i.e., a series of connected superposed cavities, of tailored proportions can be made. A scaled-down test of the method described in connection with Figure l was made and a series of connected superposed cavities of the type and proportions shown in Figure 1 was formed.

While the recirculated brine and fresh water can be introduced into the salt bed in a non-horizontal direction, somewhat better control of cavity formation is obtained Aby directing the major proportion of the water into the bed in a horizontal direction. It is advantageous to use horizontal injection when the superposed cavities are spaced very closely together such that there is little, if any, constriction between the series of connected cavities. When such closely spaced cavities are formed the use of horizontal injection does not agitate and mix together the incoming water and brine with the saturated brine in the lower cavity. Since saturated brine is the heavier it will not ordinarily mix with incoming water or unsaturated brine unless some means of agitation is used, and by employing the horizontal injection, agitation is avoided and the cavity size and proportions can be more closely controlled. The nozzle ports through which the Water and recirculated brine are injected can4 be rotated in substantially a horizontal direction so as to minimize roughness in the cavity side Wall, if desired. This can be effected by use of a rotating nozzle at the bottom of the inlet conduit or by rotating the inlet conduit itself. Better control of the cavity proportions can also be achieved by gradually raising, during the formation of an individual cavity within the series, the inlet and outlet conduits at a gradual and constant rate. The neck-like constrictions between each of the individual superposed cavities can be eliminated by raising the level of the inlet nozzle ports to approximately the level of the saturated brine in the lower cavity. Thus, a long cylindrical shaped cavity, which is actually a series of individual superposed cavities free of neck-like constrictions between the individual cavities, can be made. While Figure 1 shows the use of concentric inlet and outlet conduits, it is not essential that they be concentric and they can in fact be displaced horizontally from each other. When they are not concentric, the individual superposed cavities formed .will be connected by two channels rather than one.

Rather than having the water and recirculated brine inlet nozzles below the point at which brine is removed from the cavity, end positions can be reversed without departing from the invention.

Other equivalent forms of the invention, which has been illustrated in nonlimiting form in Figure 1, will be apparent to those skilled in the art. What is claimed is:

1. A method of cavity formation in subterranean salt beds which comprises: l) providing inlet and outlet conduits to the salt bed; (2) forming a cavity by the steps of: introducing Water via said inlet conduit into the salt bed and dissolving salt therefrom to form brine and the beginning of a cavity, removing brine from the forming cavity via said outlet conduit and repeatedly recirculating brine via the inlet conduit to the forming cavity, the total amount of water used being suiiicient to form a cavity of the desired diameter, continuing said recirculation until all of the water has been introduced and the recirculated brine has become saturated with respect to salt, thereafter discontinuing said recirculation and permitting saturated brine to remain in the cavity which has been formed; (3) elevating within the salt bed said inlet and outlet conduits to points above the level of the saturated brine in the formed cavity and forming at least one other cavity above the previously formed cavity by the steps set forth in (2) herein; and (4) removing saturated brine from the cavities formed whereby a plurality of connected superposed subterranean cavities are formed in the salt bed.

2. The method of claim 1 wherein a portion of the total water used, in forming each cavity, is introduced via the inlet conduit'into the forming cavity together with recirculating brine.

3. The method of claiml wherein the major portion of the water and recirculated brine is emitted in a substantially horizontal direction through nozzle ports into the salt bed.

4. The method of claim 3 wherein the nozzle ports are rotated in a substantially horizontal plane While water and recirculated brine are being introduced to form the cavity.

5. The methodpof claim l wherein the inlet and outlet conduits are comprised of concentric casings.

6. The method of claim 1 wherein after an individual cavity containingA saturated brine is formed, the inlet and outlet conduits are elevated, said inlet conduit being elevated to approximately t-he level of the saturated brine in the formed cavity.

7. The method of claim l wherein after an individual cavitycontaining saturated brine is formed, the inlet and outlet conduits are elevated a distance approximately equal to the radius of the cavity formed.

8. The method of claim l wherein both the inlet .and outlet conduits are slowly raised during the formation of a given cavity.

9. The method of cavity formation in subterranean salt beds which comprises: l) providing concentric inlet and outlet conduits to the salt bed; (2) forming a cavity by the steps of: introducing water in a substantially horizontal direction into salt bed via the inlet conduit and dissolving salt from the bed to form brine and begin formation of a cavity, removing brine from the forming cavity at a point above that at which the water is introduced and passing brine out from said cavity via the outlet conduit, recirculating said brine together with water via the inlet `conduit to the forming cavity until the recirculated bri-ne becomes saturated with respect to salt, the total amount of water used being suicient to form a cavity of the desired diameter, thereafter discontinuing said recirculation and permitting saturated brine to remain in the cavity which has been formed; (3) elevating the concentric inlet and outlet conduits to points above the level of the saturated brine in the cavity and forming at least one other cavity above the previously formed cavity by the steps set forth in (2) herein; and (4) removing saturated brine from the cavities formed whereby a plurality of superposed subterranean cavities are formed y in the salt bed.

l0. The method of claim 9 which is further characterized by raising Vboth the inlet and outlet conduits a distance lapproximately equal to the diameter of the formed cavity prior to initiating the introduction of water to form the next higher cavity.

References Cited in the le of this patent UNITED STATES PATENTS 

